Published: Sun, April 16, 2017
Research | By Jennifer Evans

Scientists develop solar-powered device that can harvest water from dry air

Scientists develop solar-powered device that can harvest water from dry air

While the material has a high affinity for water molecules, it easily releases the concentrated water with a slight change in temperature. Video by Roxanne Makasdjian and Stephen McNally, UC Berkeley. After all, dehumidifiers make sure that a room or home does not easily grow mold by sucking out the moisture from the air, and at the end of the day, you will have to pour all of the water away somewhere else.

The prototype of the water harvester with 2.2 pounds of MOF, under conditions of 20 to 30 percent humidity, was able to pull three quarts of water from the air in a 12-hour period. He then resorted to Evelyn Wang, a mechanical engineer from MIT in Cambridge, who had worked with him on a previous project involving MOFs. The vapor condenses as liquid water and drips into a collector'. MIT photo by Hyunho Kim. The team says the device could easily be scaled up to produce enough water to meet the daily needs of a household. Normally, harvesting pure water from thin air is an expensive procedure. These metals with organic particles create a hard but porous design that can hold liquids and gasses. In the last 20 years, researchers have created over 20,000 different MOFs for a wide variety of applications, such as separating methane and water from other gasses. They can be carefully created to pick up specific metals and organic compounds as they are holding onto more complex gasses.

To collect the water, scientists turned to metal organic frameworks, or MOFs. These are the building blocks that Yaghi stitches together into crystalline sponges using what he calls reticular chemistry. The yellow balls represent the porous spaces that can fill up with water. UC Berkeley, Berkeley Lab image.

One way of providing drinking water to people in parts of the world where it's not readily available is to give them the tools to literally suck it out of the air. The crystals are compressed between a solar absorber and a condenser plate, and the set-up is placed inside a box which is open to the air. The zirconium/adipic acid MOF is well-suited to capturing water molecules in the air, and the researchers combined it with a water storage system to create their device. In the morning, the chamber is closed, and sunlight entering through a window on top of the device then heats up the MOF, which liberates the water droplets and drives them-as vapor-toward the cooler condenser.

In a paper published to the journal Science, the MIT researchers revealed a solar-powered harvester that works on ambient sunlight.

But their ability to serve as water harvesters is a relatively new concept, Wang said. For example, the current MOF can absorb 20 percent of its weight in water. Spongy materials such as silica gels can extract moisture from the air even at low relative humidity. What powers this water harvester? MIT Technology has built a device that can produce water from the dry air. She and her colleagues built a water extraction device based on a material called a MOF, a mixture of metal and organic molecules. Yaghi said, "A person needs about a [330ml] can of water per day". "That can give you a household of water per four people per day".

The study was partly funded by ARPA-E, a US Government agency that claims to advance high-potential, high-impact energy technologies in their early stages of development.

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